Semiconductor devices have been applied to communication systems, networks, computers, electronic appliances, business machines, cameras, or even game machines. There is a great demand for semiconductor devices in various applications, such as industrial machines, peripheral tools and portable machines. With the rapid development of electronic industry, a semiconductor device is required to have a compact size, multiple pins and a low profile, without compromising functionalities and fabrication cost.
In order to achieve the objectives of having a compact size, multiple pins and a low profile, a flip-chip type of semiconductor device, which is derived from a conventional wire bonding type of semiconductor device having gold wires to connect a substrate with a chip, is designed to have no gold wires and is becoming the main stream of semiconductor device.
As shown in FIG. 1, a metal bump 210 is formed on a chip pad 201 of a chip 200, to electrically connect a solder pad 101 of a substrate 100 to the chip pad 201 of the chip 200 by heat melting or compressing processes. Typically, the solder pad 101 is formed by a circuit patterning process, such as a dry etching process and a wet etching process. The dry etching process ensures that the solder pad 101 has a precise size, but it is time-consuming. Therefore, the wet etching process, which has the advantages of low costs and fast fabrication, is becoming more popular in the circuit patterning process.
The wet etching process employs a strong acid or strong alkali etchant to perform a chemical reaction on surface molecules on a metal layer to be etched by diffusion effect, so as to complete an etching removal. However, with the wet etching process being an isotropic etching process and the metal layer being in contact with the etchant during the wet etching process, a circuitry formed on the metal layer is severely deformed. Hence, with a semiconductor chip being mounted on the substrate 100 and the solder pad 101 and the chip pad 201 being compressed, the metal bump 210 is likely to be of a flat shape due to the compression, as shown in FIG. 2. Thus, the bonding strength between the solder pad 101 and the chip pad 201 is reduced. The time taken for the metal layer to come into contact with the etchant can be reduced by increasing the etching rate, but the metal layer has to be of a reduced thickness accordingly. The metal layer is confronted with a reliability problem such as the ease strip of the circuitry.
Therefore, it is desirable to provide a substrate having its solder pads well connected so as to overcome the drawbacks of the prior art.